The present invention relates to novel, single-component, humidity-curing caulking and sealing substances based on mercapto-terminated polymers and/or oligomers, so-called polysulfides.
Compositions known in the art are extendable at room temperature and cure into a rubber-elastic product; they are highly significant in industrial sealing and bonding applications wherein the bonding or sealing site must be elastic.
The materials are mostly used in the form of two-component systems; namely, the compound with terminal mercapto groups on one hand and the oxidizer on the other are packed and stored separately, and then the two components are mixed together shortly before use. For simpler and more reliable applications, more and more users increasingly desire single-component compounds; that is, mixtures that are capable of remaining stable in storage which simultaneously contain the polymer and the oxidizer and which will harden when put to use upon contact with the atmospheric humidity at room temperature.
Single-component systems based on such various oxidizers as alkaline earth peroxide, zinc peroxide, chromate, alkali permanganate or lead dioxide are known. Each such system offers specific advantages, but also incurs specific drawbacks. At present, the best industrial single-component caulking and sealing substances based on mercapto-ended compounds contain manganese dioxide as the oxidizer.
In their cured state, the compositions based on manganese dioxide are soft, permanently elastic substances nevertheless exhibiting high resiliency properties, and even when aging, they undergo no significant stiffening.
Regrettably, however, manganese dioxide does not permit the manufacture of white compounds. This drawback is a significant problem because the user, and in particular the architect, increasingly needs white, single-component sealants.
Corresponding single-component systems are already known whereby white substances can be prepared.
Illustratively U.S. Pat. No. 3,349,047 discloses white polysulfide masses using an alkaline earth peroxide, as a rule calcium peroxide, as a latent hardener. However such substances have been found to be too stiff after curing for many applications. The attempt already has been made to lower the elastic modulus of these substances by simultaneously employing monofunctional mercapto compounds as so-called chain stoppers. Problems arise, however, as this entails reduction of the internal strength and resiliency of the product.
Other white products are known. Thus, U.S. Pat. Nos. 3,275,579; 3,402,155; 3,499,864 and German OLS 18 00 982; 20 62 259 and 21 07 971 disclose white, single-component polysulfides containing zinc oxide or zinc peroxide as hardeners. While they differ always in the kind of activator used for the oxidizer, they nevertheless all share the same basic difficulty; that is, the cured substances harden further by undesired secondary reactions during aging and become too stiff. Moreover, this problem cannot be overcome by adding plasticizers to the composition.